#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define rng(i,c,n) for(int i=c;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define fi first
#define se second
#define pb push_back
#define sz(a) (int)a.size()
#define vec(...) vector<__VA_ARGS__>
#define _3PGDklf ios::sync_with_stdio(0),cin.tie(0)
typedef long long ll;
using pii=pair<int,int>;
using vi=vector<int>;
void print(){cout<<'\n';}
template<class h,class...t>
void print(const h&v,const t&...u){cout<<v<<' ',print(u...);}
// e
signed main(){
_3PGDklf;
int n;
cin>>n;
std::map<int,int> mp;
rep(i,n){
int v;
cin>>v;
mp[v]+=1;
}
int now=0;
per(i,500011){
now+=mp[i];
if(i<=now){
print(i);
return 0;
}
}
}
